The secreted growth factor pleiotrophin (PTN) acts on endothelial as well as epithelial cells and fibroblasts and it can drive tumor growth, angiogenesis, invasion as well as metastasis. Recently, we identified a receptor for PTN, the orphan tyrosine kinase anaplastic lymphoma kinase, ALK that shares homology of its kinase domain with the insulin receptor family. ALK and PTN are overexpressed in a majority of human cancers samples whilst a series of normal tissues showed no detectable receptor expression. Ribozyme-mediated reduction of ALK in glioblastoma and other tumor cells resulted in a "gene dose"-dependent reduction of xenograft tumor growth in mice and supports ALK as a valid target for drug discovery. Recently we identified small-molecule drugs that inhibit the PTN-stimulated ALK kinase in cultured cells at nanomolar concentrations and we used homology modeling to generate a 3D model of the protein with these drug candidates. We hypothesize that it will be possible to identify novel selective inhibitors and propose the following aims: Aim 1, Lead identification: We will identify in silico novel ALK kinase inhibitors using de novo drug design, library screening and virtual combinatorial library generation. The best candidates will be synthesized for the biologic assays. Aim 2, to study the inhibition of PTN-stimulated ALK kinase activity in comparison to other growth factor-induced receptor kinase activity by these candidate inhibitors. Additional molecular modeling using these data will then be used to design and optimize inhibitors. Aim 3, Lead optimization: To improve lead compounds emanating from the biologic assays by further refinement of the molecular modeling of drug / protein interaction. These new inhibitors will then be assayed against PTN-stimulated ALK kinase activity in intact cells. Aim 4: To study the efficacy and potency of the best inhibitors on cell growth. Selected inhibitors of the PTN-stimulated ALK kinase will be tested for their ability to block PTN-induced cell proliferation, anti-apoptosis and soft agar colony formation in comparison to their blockade of other growth factors. In summary, we propose the design and study of structure-based inhibitors of the PTN/ALK signaling as a close collaboration between a biology and a molecular modeling/chemistry laboratory with the purpose of discovering novel anticancer drugs. [unreadable] [unreadable]